Great concern has developed over the reduced capacity of available disposal sites for radiation-contaminated waste from nuclear power plants. The quantity of low-level radiation-contaminated waste has begun to saturate the available capacity of permanent disposal sites. If decent burial is to be made of this material in the future, some means of drastically reducing its volume will be required.
The need for volumetric reduction instinctively stimulates the conscious mind to visualize some form of combustion, or incineration, of this type of waste. Present combustion practices have been examined, including controlled air, multiple-chamber, and fluid bed designs. In each case, the evaluations considered how each design met four fundamental combustion criteria which have been employed to supply utility and industrial boilers and industrial incinerators. Effective, complete, safe combustion requires sufficient residence time, high temperature, turbulence, and excess air. An excess air condition exists any time there is a supply of air available to the combustion process which is oreater than the amount required for 100% stoichiometry. Further, low-level radioactive waste requires special condsiderations because of its wide range in heating value, variable form, and hazardous nature.
Typical low-level radioactive contaminated wastes consist of liquid concentrates, resin slurries and sludges, and dry combustible solids. The heating value of these wastes vary from zero, for the liquid concentrates, to as much as 19,000 Btu/lb. for dry solids. Complete combustion, or evaporation, of the wastes having this calorific range presents a challenge in balancing sufficient combustion air, supplemental fuel, and quantity of waste input at all times.
The varying form of radioactive wastes is also a concern since wide ranges of waste particle size and density must be accommodated. These wastes can range from light dry solids, such as shredded paper and cloth weighing 20 lbs/cu.ft., to heavier and much smaller resin beads weighing 60 lbs/cu.ft. The hazardous nature of the waste dictates that safety in its processing be a paramount design consideration.
After a gathering, or collecting, system has been provided to select the radiation waste from multiple sources of a nuclear installation, a subsystem must be provided to reduce the form of the waste into a satisfactory form of feed for an incinerator. The incinerator must be provided with a parallel supply of conventional fuel to insure the continuous combustion of the radiation waste. The form of incinerator must provide a flow path for the waste and supplemental fuel which will result in maximum volume reduction of the waste. Finally, the supplemental, conventional fuel must be controlled to insure consistent, satisfactory combustion conditions within the incinerator as the calorific value of the wastes fluctuates.